Refrigerant Lubricated Bearings

ABSTRACT

A cooling system and methods of employing the same includes a refrigerant cycle for cycling refrigerant from a compressor to a condenser and from the condenser an evaporator, and a lubrication cycle having at least one lubricating refrigerant supply line for providing refrigerant as lubricant to a bearing assembly. The lubricating refrigerant supply line including one or more filters, such as particle filters, acid filters, or desiccant filters.

PRIORITY CLAIM

This application claims the benefit under 35 U.S.C. § 119(e) of theearlier filing date of U.S. Provisional Patent Application No.62/771,625 filed on Nov. 27, 2018 the disclosure of which isincorporated by reference herein.

FIELD

The present invention relates to cooling systems and to methods foroperating such a cooling system.

BACKGROUND

Cooling systems, such as a chiller or air conditioning system, generallyinclude a compressor, a condenser, an expansion device and anevaporator, which are connected into a so-called cooling cycle orrefrigerant cycle. In the cooling cycle refrigerant is cycled from atleast the compressor for compressing gaseous refrigerant to thecondenser for condensing gaseous refrigerant to liquid refrigerant, fromthe condenser to the expansion for expanding the liquid refrigerant,from the expansion to an evaporator for evaporating the liquidrefrigerant to gaseous refrigerant, and from the evaporating back to thecompressor. Usually, such a cooling system removes heat from a liquidvia the vapor-compression refrigerant cycle. The cooled liquid may thenbe used to cool air (e.g., air conditioning) or in an industrialprocess. A compressor of a cooling system typically employs bearingsthat require lubrication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic drawing of aspects of an exemplarycooling system in accordance with this disclosure, and

FIG. 2 illustrates a schematic drawing of aspects of an exemplarycooling system in accordance with this disclosure.

FIG. 3 illustrates a schematic drawing of aspects of an exemplarycooling system in accordance with this disclosure, and

FIG. 4 illustrates a schematic drawing of aspects of an exemplarycooling system in accordance with this disclosure.

DETAILED DESCRIPTION

Disclosed are one or more preferred embodiments that incorporatefeatures of this invention. The disclosed embodiment(s) merely exemplifythe invention. The scope of the invention is not limited to thedisclosed embodiments. Rather, the invention is defined by the claimshereto.

FIGS. 1-4 illustrates interrelated aspects of an exemplary coolingsystem 100 having a cooling cycle 10 (indicated by thick arrows) and alubrication cycle 20 (indicated by hollow arrows), wherein thelubrication cycle 20 also comprises refrigerant as lubricant.

An exemplary cooling system 100, such as a chiller or air conditioningsystem, generally includes in a cooling cycle 10 a compressor 12, acondenser 14 and an evaporator 16. Optionally there is also an expansion(not particularly illustrated), e.g., an expansion valve upstream ofevaporator 16, which may be used for reducing pressure of therefrigerant in the cooling cycle 10.

As can be seen in the cooling cycle 10, compressor 12 compresses gaseousrefrigerant which may be directed to condenser 14 to condense gaseousrefrigerant into liquid refrigerant. Liquid refrigerant is then guidedto evaporator 16 for evaporating liquid refrigerant to gaseousrefrigerant, which is then transported back to compressor 12 forproviding compressed gaseous refrigerant in a continuous cycle.

Compressor 12 itself comprises bearing assembly 2 with one or morerolling bearings. Bearing assembly 2 is schematically illustrated inFIGS. 1-4. Bearing assembly 2 may require lubrication during operation.In accordance with this disclosure, a cooling system, e.g., 100, usesrefrigerant not only in cooling cycle 10, but also in lubrication cycle20 for lubricating bearing assembly 2 using refrigerant as lubricant forbearing assembly 2.

As illustrated in FIG. 1, a portion of refrigerant is branched off fromcondenser 14 by a lubricating refrigerant supply line 22 and transportedto bearing assembly 2 in compressor 12 thereby providing lubricatingrefrigerant to bearing assembly 2. Lubricating refrigerant is introducedinto bearing assembly 2, usually under relatively high-pressure througha nozzle or injection device (not particularly illustrated), and exitscompressor 12 via lubricating refrigerant feedback line 30 for feedingback lubricating refrigerant to the evaporator 16.

Since a first pressure level of condenser 14 is much higher than asecond pressure level of evaporator 16, there is no need for anadditional lubricating refrigerant propelling, such as a pump, fortransporting lubricating refrigerant through lubrication cycle 20. Inorder to prevent reflux of lubricating refrigerant to condenser 12, acheck valve 25 is disposed within lubricating refrigerant supply line 22upstream of compressor 12, as illustrated in FIG. 1.

Bearings, e.g., 2, in compressors of cooling systems, e.g., in chillersor air condition systems, are often lubricated by the refrigerant usedin the cooling system itself, as in exemplary embodiments illustrated inFIGS. 1 and 2. However, refrigerant may contain harmful products whichmay lead to corrosion or cause other damages to bearing, e.g., 2.Refrigerants used in air conditioning chillers are often not stableunder all conditions. Molecules can break down and produce by-productcompounds which are harmful to chillers and bearings, e.g., 2, used inthe chiller compressor. Breakdown can be caused by heat, pressure or thepresence of liquid contaminants that functions as catalysts or byinherent chemical instability of such refrigerant. Particularly damagingby-products are acids, in particular hydrofluoric acid (HF) andhydrochloric acid (HCl), which are very corrosive. HF and HCl are formedby fluorine and chlorine atoms contained in the refrigerant molecules.Of special concern are recently developed refrigerants such as R1234ze,R1233zd and R1234yf, which are formulated to break down easily in casethey are leaked into atmosphere where they can potentially causeenvironmental problems.

Water is another liquid contaminant that can break down and produceby-products that can corrode or diffuse into bearing components. Acombination of water, HF, HCl and oxygen from entrapped air is a harmfulmixture that causes severe damage to bearings. However, water itself isalso problematic since it provides for poor lubrication and can causecorrosion and hydrogen embrittlement of steel components of bearings,e.g., 2.

It is therefore object of this disclosure, to provide a possibility forprotecting a refrigerant lubricated bearing from harmful influence ofby-products that cause corrosion or other damages.

For protecting bearing, e.g., 2, from harmful substances in refrigerant,upstream of the bearing assembly, a refrigerant supply line, e.g., 22,further comprises at least one filter, e.g., 24, 25, 26, 28, forfiltering lubricating refrigerant. Such a filter contains material whichabsorbs, adsorbs and/or reacts with contaminants and/or by-products, sothat refrigerant used for lubricating bearing, e.g., 2, is substantiallyfree of harmful substances.

Because refrigerant is used as refrigerant in cooling cycle 10 (as wellas lubricant in lubricating cycle 20), refrigerant is exposed to severalmechanical components (e.g., compressor, condenser, evaporator,connecting lines) and thus exposed to heat and pressure, as well as toliquid and/or gaseous contaminants (e.g., air and moisture), which maycause molecules in a refrigerant to break down and produce byproductcompounds that are harmful to bearing assembly 2 used in compressor 12.Additionally, the breakdown of molecules may even be caused by aninherent chemical instability of a refrigerant itself, depending on therefrigerant chosen. Furthermore, particles, e.g., originating from wearor abrasion of mechanical components, may be present in refrigerant andwhich may be harmful for bearing assembly 2 when such refrigerant isused as lubricant. Such byproducts and/or particles may be very harmfulto a refrigerant lubricated bearing assembly as they may lead tocorrosion, increased wear, insufficient lubrication conditions, orotherwise cause damage in a bearing assembly, e.g., bearing assembly 2.

Consequently, there may be an arrangement of filter s 24, 26, and 28 (asin FIGS. 1 and 3), or an arrangement of individual and combined filter s25, 28 (as shown in FIGS. 2 and 4) arranged in the lubricatingrefrigerant supply line 22 upstream of the bearing assembly 2. Thefilter (s) 24, 25, 26, 28 contain materials that may absorb or reactwith the byproducts, contaminants and/or particles, thereby removingparticles, acids, or water and the like from refrigerant within coolingsystem 100.

Filter s, e.g., 24, 25, 26, 38, may adsorb, catch, or trap certainmolecules from refrigerant by mechanical, chemical, and/or physicaladsorption, depending on filter material type, surrounding environmentcomposition, or an expected type of contaminant.

Highly damaging byproducts are acids, in particular hydrofluoric acid(HF) and hydrochloric acid (HCl), which are highly corrosive.Hydrofluoric acid and hydrochloric acid are formed by fluorine andchlorine atoms contained in the refrigerant itself. Of particularconcern are recently developed refrigerants such as R1234ze, R1233zd andR1234yf, which are formulated to break down easily in case they areleaked into the atmosphere where they can potentially causeenvironmental problems. Such breakdown ensures that an environment isnot harmfully contaminated by the refrigerant. Consequently, one of thefilter units, e.g., filter unit 24 illustrated in the exemplaryembodiments of FIG. 1, is an acid filter for filtering hydrofluoricacids and/or hydrochloric acids from refrigerant, wherein a filteringmaterial of an acid filter, e.g., 24, may include Alumina (Al₂O₃),Silica (SiO2), Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO),Aluminosilicate (Al2SiO5) and/or combinations thereof. Such filtermaterials have proven successful for filtering hydrofluoric and/orhydrochloric acids. Aluminum or aluminum compounds are preferably usedfor the hydrofluoric acids, as products of a reaction of aluminum andhydrofluoric acid is aluminum fluoride, a solid crystalline material,which may easily be removed. For adsorbing hydrochloric acids, a filtercontaining magnesium oxide is preferred, as reaction products of areaction of HCl and magnesium oxide are magnesium chloride and water.Upon reading this disclosure in its entirety, one will appreciate thatother suitable filter materials may be used.

In FIGS. 1 and 3, a second filter unit 26 is a desiccant filter forremoving water (dissolved and/or free water) and/or moisture from therefrigerant. A filtering material of a desiccant filter, e.g., 26, isusually hygroscopic and may include Zeolite Scavenger sorbents, such ascalcium zeolites, sodium zeolites, potassium zeolites, magnesiumzeolites and combinations thereof, with all sizes and shapes, andgraphene oxide, and combinations thereof for filtering dissolved water,and polymers, such as water absorbing filter, for filtering free water.Water or rather moisture and humidity has been identified as anotherliquid contaminant which react with the refrigerant so that therefrigerant may break down and produce byproducts that may corrode ordiffuse into bearing components. Therefore, a combination of water,hydrofluoric acid, hydrochloric acids and/or oxygen from entrapped air,is a very harmful mixture that can cause severe damage to the bearingassembly.

The third filter unit 28 in turn is in the illustrated embodiment ofFIGS. 1-4 a particle filter, which removes particles, e.g. particlesoriginating form wear or abrasion of mechanical components, from thelubricating refrigerant. These particles are harmful to the surfaces ofthe bearing assembly, e.g., to races of bearing rings or rollingelements, and may lead to increased wear and insufficient lubricationconditions in the bearing assembly 2.

Besides the arrangement of filter units as illustrated in FIGS. 1 & 3,it is also possible to combine some or all filter units for reducing theoverall required space or to use synergistic effects. Such embodimentsare illustrated in FIGS. 2, 4, where the filter unit 25 is a combinationof an acid filter and a desiccant filter. This is particularlypreferably, as some of the adoption reaction of acids are competitive tothe adsorption of water/moisture, or as mentioned above the reactionproduct of the chemical reaction may be water, which also needs to beremoved from the refrigerant.

In summary, by using a filter arrangement for filtering harmfulsubstances from the lubricating refrigerant, before the refrigerant isused for lubricating the bearing assembly, a lubricating refrigerant maybe provided which is substantially free of harmful components. Thereby,the service life of the bearing assembly and the cooling system may beincreased, as the lubricating conditions of the bearing assembly areimproved.

As discussed above, it is possible to combine some or all filters forreducing overall component size and according a required space, or touse synergistic effects. For example, as illustrated in FIGS. 2 & 4,exemplary filter 25 is a combination of an acid filter and a desiccantfilter. This is particularly useful as some reaction products of acidsare competitive to adsorption of water/moisture, or as mentioned above areaction product of a chemical reaction may be water, which should beremoved from cooling system, e.g., 100, refrigerant.

As illustrated in FIGS. 3 and 4, an accumulator 40 may be arranged inlubricating refrigerant supply line 22, 23. Accumulator 40 is configuredto ensure that a constant lubricating refrigerant supply is provided atcompressor 12 even if pressure in supply line 22, 23 fluctuates.Consequently, accumulator 40 works as auxiliary reservoir forpressurized refrigerant, which may be fed to bearing assembly 2 ifinsufficient lubricating refrigerant supply is present in lubricatingrefrigerant supply line 22, 23.

Accumulator 40 usually has two compartments 42, 44, wherein topcompartment 42 is filled with a gas or may contain a spring, which isadapted to provide a preload/load 46 onto a piston or bladder 48, whichseparates compartments 42, 44. Second compartment 44 is used for storingpressurize refrigerant. Such an accumulator 40 works as follows: at astart of a lubrication cycle, second compartment 44 of accumulator 40 isempty. As pressure builds up, second compartment 44 starts to fill upwith liquid refrigerant. Pressure is balanced by pressure 46 of acompressed gas in first compartment 42 or by compression of a spring, ifused. At steady state operation compartments 42, 44 each haveapproximately a same volume. This is controlled by selection of gaspressure or spring force 46 in first compartment 42.

A volume of pressurized liquid refrigerant in second compartment 44serves as reserve lubricant in case of malfunction of a system, e.g.,100, for any reason, e.g., in a case of an unexpected pressure drop.

Lubricating refrigerant supply branch 22 may be branched off of acondenser, e.g., 14, as explained above, or may alternatively or inaddition be branched off from an optional economizer. In case aneconomizer is present in the cooling cycle, it may be preferred to userefrigerant from an economizer with a lower pressure differential to anevaporator pressure level in order to lubricate a bearing assembly,e.g., 2. Thus, a choice of refrigerant type, low or medium pressure, thenumber of compressor stages and using or not using an economizer areeconomic considerations. The use of an economizer is particularlyadvantageous in case compressor 10 is a high-speed compressor whichprovides very high pressure to refrigerant which might be too high forlubricating bearing assembly 2. In such a case a pressure differencebetween an economizer and an evaporator can be configured to remain highenough for transporting refrigerant through lubricating cycle 20 andprovide sufficient refrigerant at bearing assembly 2 for lubricating.

FIG. 4 illustrates exemplary embodiments in accordance with thisdisclosure. In addition to a cooling system as illustrated in FIG. 1, acooling system 100 as in FIG. 2 has a first lubricating refrigerantsupply branch 22-1, which branches off from condenser 14 or aneconomizer (not particularly illustrated, but downstream from condenser14 and upstream from evaporator 16), and a second lubricatingrefrigerant supply branch 22-2 which branches off from evaporator 16.First and second lubricating refrigerant branches 22-1, 22-2 merge intoa main lubricating refrigerant supply line 23. Second lubricatingrefrigerant supply branch 22-2 may be used at startup for providing aliquid refrigerant to compressor 12 even before compressor 12 startsoperating. A pump 50 may be arranged in second refrigerant supply line22-2 which transports liquid refrigerant from evaporator 16 tocompressor 12. Since pump 50 is only operated during startup, energyconsumption of cooling system 100 is not unduly increased relative toknown systems with a constantly operating pump. Additionally, pump sizemay be reduced as only a small amount of refrigerant needs to betransported to compressor 12 in a pre-lubrication cycle. In order toavoid any reflux of refrigerant to evaporator 16, particularly duringordinary operation of a cooling system, e.g., 100, a further check valve27 is arranged in second lubricating refrigerant supply line 22-2.

Pump 50 may be a positive displacement pump and may also be used tocontrol flow during ordinary operation, e.g., in case a pressuredifference is fluctuating or a pressure difference is too low or toohigh. Positive displacement pumps have a close correlation betweenrotational speed and flow rate and are less affected by a pressuredifference than ordinary dynamic pumps. It is further possible that thepump is a so-called rotary vane pump, which has advantages over knownpumps as a they may also be used for pumping a mixture of gaseous andliquid fluids, which may be present in evaporator 16.

A cooling system 100 in accordance with FIG. 2 embodiments works asfollows.

At startup of a cooling system, liquid refrigerant for lubrication isavailable in evaporator 16. As system pressure is building up, liquidrefrigerant becomes available in condenser 14. Lubricating refrigerantpump 50 is first pumping refrigerant from evaporator 16, then aftercondenser 14 and evaporator 16 have reach a first pressure differencelevel, the source of liquid refrigerant is switched to condenser 14.Downstream from pump 50, refrigerant is supplied to bearing assembly 2for lubrication through a nozzle, then drains from bearing assembly 2 toevaporator 16 by feedback line 30. In high speed compressors 12, anozzle produces a jet that spays refrigerant into bearing assembly 2.Pressure drops through such a nozzle, which may be used to controlrefrigerant flow. In low speed compressors 12, jet injection may not benecessary, and refrigerant can flow into and through bearing assembly 2without pressure drop. In such a case pump 50 may also function as ametering device.

In summary cooling systems in accordance with this disclosure have thefollowing advantages:

Lubricating refrigerant flow is provided by a pressure differencebetween condenser, e.g., 12, and an evaporator, e.g., 16, instead of apump. This reduces overall costs of a cooling system and increasesoverall reliability of the system.

Lubricating refrigerant flow has minimal variations due to use of anaccumulator which ensures that lubrication of a bearing assembly, e.g.,2, is continuously provided. Additionally, interruptions of lubricatingrefrigerant flow are minimized and controlled. Since a pump is only usedat startup (if at all) or if for any reason a pressure differentialbecomes too low, pump wear is minimized and additional power consumptionis reduced. By using a rotary vane type pump internal leakage isminimized and pressure is created independently of speed. By using avariable speed drive for a pump, it is further possible to start such apump at low speed for avoiding problems with cavitation, which usuallyoccur when a mixture of liquid and gaseous fluids needs to be pumped. Bynot using the pump at steady-state conditions, overall energyconsumption of the cooling system is reduced. By using a desiccant, acidand/or particle filter 25 in the lubricating refrigerant flow, a bearingassembly's exposure to harmful substances which may corrode the bearingcomponents is also minimized.

A first exemplary cooling system: A cooling system includes arefrigerant cycle for cycling refrigerant from at a compressor in orderto compress gaseous refrigerant to a condenser for condensing gaseousrefrigerant to liquid refrigerant, from the condenser to an evaporatorfor evaporating the liquid refrigerant to gaseous refrigerant, and fromthe evaporating back to the compressor, and a lubrication cycle havingat least one lubricating refrigerant supply line for providingrefrigerant as lubricant to a bearing assembly, and the at least onelubricating refrigerant supply line branches off from the refrigerantcycle at the condenser for providing refrigerant to the bearingassembly, and rees with the refrigerant cycle at the evaporator, forfeeding back refrigerant from the bearing assembly to the refrigerantcycle.

A second exemplary interrelated cooling system includes a refrigerantcycle for cycling refrigerant from at least a compressor for compressinggaseous refrigerant to a condenser for condensing gaseous refrigerant toliquid refrigerant, from the condenser to an economizer for lowering apressure of the gaseous refrigerant, from the economizer to anevaporator for evaporating the liquid refrigerant to gaseousrefrigerant, and from the evaporating back to the compressor, and alubrication cycle having at least one lubricating refrigerant supplyline for providing refrigerant as lubricant to a bearing assembly, andthe at least one lubricating refrigerant supply line branches off fromthe refrigerant cycle at the economizer and/or at the compressor forproviding refrigerant to the bearing assembly, and rees with therefrigerant cycle at the evaporator, for feeding back refrigerant fromthe bearing assembly to the refrigerant cycle.

A third interrelated exemplary cooling system includes the lubricatingrefrigerant supply line terminating in at least one nozzle orrefrigerant injection device, which is adapted to provide and directlubricating refrigerant to the bearings assembly in the compressor.

A fourth interrelated exemplary cooling system includes the lubricationcycle has a first lubricating refrigerant supply branch branching offfrom the condenser or from the economizer, and a second lubricatingrefrigerant supply branch branching off from the evaporator, which areboth adapted to supply refrigerant to the bearing assembly.

A fifth interrelated exemplary cooling system includes the first and thesecond lubricating refrigerant supply line branches merge to a singlemain lubricating refrigerant supply line upstream of the bearingassembly.

A sixth interrelated exemplary cooling system include a pump, which isarranged either in the second lubricating refrigerant supply line branchor in the main lubricating refrigerant supply line.

A seventh interrelated exemplary cooling system includes at least onefilter 25 is arranged in the lubricating refrigerant supply lineupstream of the bearing assembly.

An eighth interrelated exemplary cooling system includes an accumulatoris arranged in the lubricating refrigerant supply line upstream of thebearing assembly.

A ninth interrelated exemplary cooling system includes a method ofoperating a cooling system, wherein the refrigerant being used aslubricant is driven through the lubrication cycle line by a pressuredifference between the condenser or economizer and the evaporator.

A tenth interrelated exemplary cooling system includes a refrigerantlubricated bearing arrangement comprising a bearing assembly, which islubricated by refrigerant, a refrigerant supply line for supplyingrefrigerant to the bearing assembly as lubricant, wherein upstream ofthe bearing assembly the refrigerant supply line further comprises atleast one filter unit for filtering the refrigerant.

An eleventh interrelated exemplary cooling system includes the at leastone filter unit comprises at least one of an acid filter, a desiccantfilter and a particle filter.

A twelfth interrelated exemplary cooling system includes the at leastone filter unit is a combined filter unit of at least an acid filter anda desiccant filter for filtering acid and moisture from the refrigerant.

A thirteenth interrelated exemplary cooling system includes the at leastone filter unit is an filter arrangement of a plurality of filterelements comprising an acid filter, a desiccant filter or a combinationof acid filter and desiccant filter, and a particle filter, wherein theacid filter is arranged upstream of the desiccant filter and theparticle filter, and the desiccant filter or the combined filter of acidfilter and desiccant filter is arranged upstream of the particle filter.

A fourteenth interrelated exemplary cooling system includes the filterunit is adapted to adsorb, catch or trap certain molecules from therefrigerant by chemical and/or physical adsorption.

A fifteenth interrelated exemplary cooling system includes the filterunit comprises an acid filter for filtering hydrofluoric acids and/orhydrochloric acids from the refrigerant, wherein a filtering material ofthe acid filter is selected from the group of Alumina (Al₂O₃), Silica(SiO₂), Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO),Aluminosilicate (A1 ₂SiO₅) and combinations thereof.

A sixteenth interrelated exemplary cooling system includes the filterunit comprises a desiccant filter for filtering dissolved water and/orfree water from the refrigerant, wherein a filtering material of thedesiccant filter is selected from the group of Zeolite Scavengersorbents, such as calcium zeolites, sodium zeolites, potassium zeolites,magnesium zeolites and combinations thereof, with all sizes and shapes,and graphene oxide, and combinations thereof for filtering dissolvedwater, and polymers, such as water absorbing filter, for filtering freewater.

A seventeenth interrelated exemplary cooling system includes the filterunit comprises a particle filter for filtering particles from therefrigerant, wherein preferably the particle filter is a stainless steelmesh, a magnet for metallic particle and/or a combination thereof.

An eighteenth interrelated exemplary cooling system includes arefrigerant cycle line for cycling refrigerant from at least acompressor unit for compressing gaseous refrigerant to a condenser unitfor condensing gaseous refrigerant to liquid refrigerant, from thecondenser unit to an expansion unit for expanding the liquidrefrigerant, form the expansion unit to an evaporator unit forevaporating the liquid refrigerant to gaseous refrigerant, and from theevaporating unit back to the compressor unit, wherein at least thecompressor unit comprises a bearing arrangement according to any coolingsystems in accordance with this disclosure.

A nineteenth interrelated exemplary cooling system includes therefrigerant supply line branches off from the refrigerant cycle line.

It will be appreciated that the interrelated exemplary embodiments aboveare non-limiting and only provided by way of example to ease a readersunderstanding of a variety of embodiments in accordance with thisdisclosure.

According to a preferred embodiment the cooling system operates asfollows:

At startup of the cooling system, liquid refrigerant for lubrication isavailable in the evaporator. As the system pressure is building up,liquid refrigerant becomes available in the condenser. The lubricantpump is first pumping refrigerant from the evaporator, then after havingreach a certain pressure difference level, the source of liquidrefrigerant is switched to the condenser. Downstream from the pump, therefrigerant is supplied to the compressor bearings for lubricationthrough a nozzle, then drains from the bearing assembly to theevaporator. In high speed compressors, the nozzle produces a jet thatspays refrigerant into the bearings. The pressure drops through thenozzle and the nozzle controls the flow. In low speed compressors, jetinjection may not be necessary. The refrigerant can flow into thebearing housing without pressure drop, then through the bearings. Inthat case, it is also possible that the pump functions as a meteringdevice.

The optional pump may be engaged at all times, but it is preferred toengage the pump only to pump refrigerant from the evaporator at startup,then to turn it off and to only use the pressure differential betweenthe condenser (or economizer) and the evaporator to drive thelubricating refrigerant flow.

In order to keep a supply of pressurized refrigerant in reserve, in caseof a pump malfunction, a hydraulic accumulator is be filled byrefrigerant, when the pump is started, which should be in apre-lubrication cycle, before the compressor is started.

A compressor may be a centrifugal compressor which includes one or moreimpellers that compress the refrigerant. The impellers are mounted on arotating shaft which is supported by a plurality of bearings. Thebearing assembly requires a steady supply of lubricant, which is oftenoil.

A pump can be used to drive the refrigerant flow to the bearings.However, a pump may cavitate making it more difficult to supply therefrigerant to the bearings. There can also be operating conditionsunder which a supply of refrigerant provided by a pump is insufficientor a state of refrigerant is a mixture of liquid and vapor so thatbearings may not be lubricated, properly. Additionally, there is ageneral reliability problem as a flow of bearing lubricant stops, if apump for some reason stops working. A common reason why a pump stopsworking is a loss of electric power. Moreover, a pump that is constantlyengaged also wears and consumes power.

It is therefore an object of the present disclosure to provide a coolingsystem with refrigerant lubricated bearings, which is operatingreliably, and is cost-efficient.

In accordance with this disclosure some embodiments include a coolingsystem includes a refrigerant cycle for cycling refrigerant from atleast a compressor for compressing gaseous refrigerant to a condenserfor condensing gaseous refrigerant to liquid refrigerant, from thecondenser to an evaporator for evaporating liquid refrigerant to gaseousrefrigerant, and from an evaporating back to a compressor. Such acooling system further comprises a lubrication cycle having at least onelubricating refrigerant supply line for providing refrigerant aslubricant to a bearing assembly, which may be part of a compressor.

For providing a stable supply of lubricating refrigerant to a bearingassembly, in some embodiments at least one lubricating refrigerantsupply line branches off from a refrigerant cycle at a condenser forproviding refrigerant to a bearing assembly, and rees with a refrigerantcycle at an evaporator, for feeding back refrigerant from a bearingassembly to a refrigerant cycle. Thereby, a pressure difference betweena condenser and an evaporator may be used for transporting lubricatingrefrigerant in a lubricating cycle. A pressure difference results from adifference between a high pressure level of a compressor and a lowpressure level of an evaporator. This transports refrigerant through arefrigerant cycle and also through a lubrication cycle.

According to a further aspect and/or a preferred embodiment, arefrigerant cycle may also comprise an economizer.

An economizer may be used in a cooling system in accordance with thisdisclosure in a two stage (or more generally multi stage) compressor.Thereby an expansion process is separated into two (or more) steps withan economizer in-between. Hence, liquid refrigerant from a condenserenters a first expansion device, which reduces a pressure of therefrigerant. This pressure drop causes a portion of liquid refrigerantto evaporate, and a resulting mixture of liquid and gaseous refrigerantenters an economizer. Consequently, a pressure in an economizer isbetween that of a condenser and an evaporator. An economizer itself isconnected to a second expansion device and to an inlet to a second stageof a two stage compressor. In an economizer, a gaseous refrigerant isseparated from a liquid refrigerant, and only remaining liquidrefrigerant is fed to a second expansion device and further to anevaporator. A gaseous part of refrigerant in turn is recompressed by asecond stage of such a compressor, and fed back from an outlet of asecond stage compressor to a condenser. Since part of such refrigerantis already vaporized upstream of an evaporator, an amount of requiredcompressor power is reduced as a gaseous part of such refrigerantgenerated in an economizer only needs to be compressed by the secondstage impeller. In a system without an economizer, more gaseousrefrigerant would be released and more gaseous refrigerant would berecompressed in-stead of being in liquid form and evaporate before goingback to a first stage of a compressor. Thus, by using an economizer, asystem efficiency is increased (by 4% to 6%), as recompression ofgaseous refrigerant is waste of energy.

In embodiments, where an economizer is present, there is an additionalor alternative possibility to branch off a lubricating supply line froma compressor or from an economizer. Using an economizer as branch offfor a lubricating refrigerant supply line allows for a slower movementof refrigerant in a lubrication cycle and thereby for a more controlleddistribution of refrigerant to a bearing assembly. It also reduces aspeed with which refrigerant is introduced or sprayed into a bearingassembly.

A lubricating refrigerant supply line may terminate in a nozzle orinjection device for directing and introducing refrigerant to a bearingassembly. A nozzle or injection device allows for an optimized andguided provision of lubricating refrigerant to a bearing assembly, andthereby for an improved lubrication. Further, it is preferred that asupply line itself is designed such that pressure drops across a nozzlerather than throughout a supply line.

According to a further preferred embodiment, the lubrication cycle has afirst lubricating refrigerant supply line branch branching off from thecondenser and/or from an economizer, and a second lubricatingrefrigerant supply line branch branching off from an evaporator, whereinboth branches are adapted to supply refrigerant to a bearing assembly.The use of refrigerant from an evaporator is preferred at startup of acooling system. At a startup phase, refrigerant in an evaporator isliquid and can be used for lubricating bearings before a compressor isstarted, while there is no liquid refrigerant in a condenser, whichcould be used for lubricating the bearing assembly. Using refrigerantfrom an evaporator allows for a so-called pre-lubrication cycle duringwhich refrigerant is provided to the bearing assembly before thecompressor start operating. This in turn ensures a sufficientlubrication of a bearing assembly at all times. Thereby, a service lifeof a compressor may be prolonged. On will appreciate that more than twobranches may be provided.

A second branch-off from an evaporator a pump is arranged, which may beoperated at start up and provides liquid refrigerant to a bearingassembly of a compressor before operating a compressor. Use of a pumpensures that sufficient refrigerant is provided at a bearing assembly atstart up and also in case a pressure difference has not been built up ordrops during ordinary operation. Preferably, a pump is controlled suchthat it starts if a pressure differential between a condenser and/oreconomizer becomes less than a predetermined value. To avoid or minimizethe risk of cavitation in a pump suction line, a pump speed may becontrolled for slow start and/or variable speed.

A pump may be disposed in a main lubrication supply line, which isprovided by a merging of a first and second branch supply lines upstreamof a bearing assembly. A pump is preferably operated at start up only,or in order to drive a lubricating refrigerant in case of an unexpecteddrop in pressure difference. However, arranging a pump in a main supplyline might increase a flow resistance in a lubrication supply line, asrefrigerant has also to pass a pump.

According to a further preferred embodiment, the cooling system furthercomprises a filter 25 which is arranged in the lubricating refrigerantsupply line upstream of the bearing assembly. Thereby, a filter 25 maybe arranged in a main supply line and/or in one or both branchesdepending design considerations. This filter ensures that harmfulsubstances, e.g., water and/or other substances, which may occur due toa breakdown of molecules of a refrigerant due to heat, pressure and/ormechanical abrasion, are filtered out of refrigerant so that refrigerantwhich is used for lubricating a bearing assembly is not contaminated.Advantageously, a filter comprises at least one for filtering outliquids, such as water and acids, and a second for filtering outcontaminate particles.

An accumulator may be arranged in a lubrication cycle line upstream of abearing assembly. An accumulator is preferably filled up withrefrigerant at start-up and ensures that a continuous lubrication isprovided at a bearing assembly even during pressure differencevariations between a pressure level of a compressor/economizer and anevaporator. An accumulator may also serve as pressurized lubricationrefrigerant reservoir at start-up instead of a pump or in case the pumpis not working. Consequently, an accumulator is preferably adapted tooperate in a pre-lubrication cycle, before a compressor is started.

Preferably, an accumulator has two compartments, one on top that isfilled with a gas or may contain a spring, a second that is used forstoring pressurize refrigerant. Two compartments are separated by apiston or a rubber bladder.

An exemplary accumulator works as follows: at start of a relubricationcycle, a second compartment of an accumulator is empty. As pressurebuilds up, a second compartment starts to fill up with liquidrefrigerant. A pressure is balanced by a pressure of a compressed gas ina first compartment or by a compression of the spring, if used. Atsteady state operation two compartments have approximately a samevolume. This is controlled by selection of gas pressure or spring forcein a first compartment.

As mentioned above, a volume of pressurized liquid refrigerant in asecond compartments serves as reserve lubricant in case of malfunctionof a system for any reason.

In an exemplary method for operating a cooling system, a refrigerantbeing used as lubricant is driven through a lubrication cycle line by apressure difference between a condenser or economizer and theevaporator.

For protecting the bearing from harmful substances in the refrigerant,it has been proposed that upstream of the bearing assembly, therefrigerant supply line further comprises at least one filter unit forfiltering the lubricating refrigerant. Such a filter contains materialwhich absorbs, adsorbs and/or reacts with contaminants and/orby-products, so that the refrigerant, which is used for lubricating thebearing, is substantially free of harmful substances.

According to a preferred embodiment, the at least one filter unitcomprises at least one of an acid filter, a desiccant filter and aparticle filter. Thereby, particles, acids and/or water may be removedfrom the refrigerant, which are the most harmful substances for thebearing, so that the bearing is protected from corrosion and otherdefects. Commercially available desiccant filters can also be used, forexample to remove water. It is further preferred to arrange thefilter(s) as kidney filter(s) that continuously filter the refrigerantin the cooling system. However, for refrigerant lubrication of thebearing assembly it is preferred to arrange the filters in line upstreamof the bearing assembly.

Preferably, the at least one filter unit is a combined filter unit of atleast an acid filter and a desiccant filter for filtering acid andmoisture from the refrigerant. The combination of filters into e.g. onehousing reduces the required space for the additional filters. Furthersynergistic effects may be exploit by combining the filter units and forincreasing the filter's efficiency. Often, water and acid arecompetitive substances for the adsorption to the filter material. Byproviding a combined filter both, water and acid, may be equally andreliably removed. Additionally or alternatively, the filter elements maybe designed to have the same dimensions as an oil or other filterelement and may be placed in a filter housing that is already present inthe flow path of the refrigerant used for the bearing lubrication.

According to a further preferred embodiment, the at least one filterunit is an filter arrangement of a plurality of filter elementscomprising a desiccant filter, an acid filter or a combination of acidfilter and desiccant filter, and a particle filter, wherein thedesiccant filter is arranged upstream of the acid filter and theparticle filter, and the desiccant filter or the combined filter of acidfilter and desiccant filter is arranged upstream of the particle filter.The indicated filter arrangement allows for an optimized filtering ofthe refrigerant. There are for examples filters which provide a verygood adsorption of acids. However, in the presence of water theiradsorption properties deteriorate as there is a competitive bonding ofwater and acid to the filter material, wherein the affinity of thefilter material for hydrogen bonding is higher. Consequently, theremoval of water or moisture from the refrigerant upstream of the acidfilter allows for both an improved water/moisture and acid filtering. Ofcourse it is also possible to arrange the particle filter upstream ofdesiccant filter and acid filter or a combination of both, or to arrangethe filters in a still different order.

The filter unit itself is preferably adapted to adsorb, catch or trapcertain molecules from the refrigerant by chemical and/or physicaladsorption, wherein the kind of adsorption is depending on the materialtype and the surrounding environment composition. That means, when theadsorption is physical (Physisorption), the trapped molecules stay inthe same chemical structure and are adsorbed via hydrogen bonds or vander Waals bonds. In this case the interaction between the filtermaterial and the surrounding environment is reversable. Consequently,desorption, i.e. cleaning the filter, can occur, e.g. by heating thefilter material or when two molecules are in competition. On the otherhand, when the adsorption is chemical (Chemisorption), a chemicalreaction occurs between the filter material and the surroundingenvironment molecules which may generate (in some cases) new products.In this case the adsorption is strong and occurs via covalent, metallicor ionic bonding.

According to a further preferred embodiment, the filter unit comprisesan acid filter for filtering hydrofluoric acids and/or hydrochloricacids from the refrigerant, wherein a filtering material of the acidfilter is selected from the group of Alumina (Al₂O₃), Silica (SiO2),Graphite Oxide, Graphene Oxide, Manganese Oxide (MgO), Aluminosilicate(Al2SiO5) and combinations thereof. These filter materials have proofedto be efficient in filtering hydrofluoric and/or hydrochloric acids.

For removing water and/or moisture from the refrigerant it isadvantageous to use a filter unit which comprises a desiccant filter forfiltering dissolved water and/or free water from the refrigerant. Thefiltering material of the desiccant filter is preferably selected fromthe group of Zeolite scavenger sorbents, such as calcium zeolites,sodium zeolites, potassium zeolites, magnesium zeolites and combinationsthereof, with all sizes and shapes, and graphene oxide, and combinationsthereof for filtering dissolved water, and polymers, such as waterabsorbing filter, for filtering free water. These kinds of filters arecost effective, commercially available and easy to handle.

According to a further preferred embodiment, the filter unit comprises aparticle filter for filtering particles from the refrigerant, wherein afiltering material of the particle filter preferably is a stainlesssteel mesh, magnet for metallic particle and/or a combination thereof.

A further aspect of the present invention relates to a cooling systemcomprising a refrigerant cycle line for cycling refrigerant from atleast a compressor unit for compressing gaseous refrigerant to acondenser unit for condensing gaseous refrigerant to liquid refrigerant,from the condenser unit to an optional expansion unit for expanding theliquid refrigerant, form the condenser or the optional expansion unit toan evaporator unit for evaporating the liquid refrigerant to gaseousrefrigerant, and from the evaporating unit back to the compressor unit,wherein at least the compressor unit comprises a bearing arrangement asmentioned above.

Thereby it is preferred that the refrigerant supply line branches offfrom the refrigerant cycle line. This allows for a simplified design ofthe compressor and there is no need for an additional lubricationreservoir.

Further preferred embodiments are defined in the dependent claims aswell as in the description and the figures. Thereby, elements describedor shown in combi-nation with other elements may be present alone or incombination with other elements without departing from the scope ofprotection.

In the following, preferred embodiments of the invention are describedin relation to the drawings, wherein the drawings are exemplarily only,and are not intended to limit the scope of protection. The scope ofprotection is defined by the accompanied claims, only.

Further preferred embodiments are defined in the dependent claims aswell as in the description and the figures. Thereby, elements describedor shown in combination with other elements may be present alone or incombination with other elements without departing from the scope ofprotection.

REFERENCE NUMERALS

-   -   100 Cooling system    -   10 Cooling cycle    -   12 compressor    -   14 condenser    -   16 evaporator    -   20 lubrication cycle    -   22 lubricating refrigerant supply line    -   22-1 first lubricating refrigerant supply line    -   22-2 second lubricating refrigerant supply line    -   23 main lubricating refrigerant supply line    -   30 lubricating refrigerant feedback line    -   32 check valve    -   60 check valve    -   24 first filter    -   26 second filter    -   25 combined filter    -   28 third filter    -   40 accumulator    -   42 first compartment    -   44 second compartment    -   46 spring force/gas pressure    -   48 piston/bladder    -   50 pump.

We claim:
 1. A cooling system comprising a refrigerant cycle for cyclingrefrigerant from a compressor to a condenser via and from the condenseran evaporator; a lubrication cycle having at least one lubricatingrefrigerant supply line for providing refrigerant as lubricant to abearing assembly; and at least one filter coupled to the refrigerantsupply line for filtering the refrigerant upstream from the bearingassembly.
 2. The cooling system of claim 1, wherein the at least onefilter comprises at least one of an acid filter, a desiccant filter, anda particle filter.
 3. The cooling system of claim 1, wherein the atleast one filter is a combined filter unit of at least an acid filterand a desiccant filter for filtering acid and moisture from therefrigerant.
 4. The cooling system of claim 1, wherein the at least onefilter unit is a filter arrangement of a plurality of filter elementscomprising an acid filter, a desiccant filter, and a particle filter,wherein the acid filter is arranged upstream of the desiccant filter andthe particle filter and the desiccant filter is arranged upstream of theparticle filter.
 5. The cooling system of claim 1, wherein the filterunit is adapted to absorb, catch, or trap certain molecules from therefrigerant by chemical or physical adsorption.
 6. The cooling system ofclaim 1, wherein the filter unit comprises an acid filter for filteringhydrofluoric acids and/or hydrochloric acids from the refrigerant,wherein a filtering material of the acid filter comprises at least oneof Alumina (Al₂O₃), Silica (SiO2), Graphite Oxide, Graphene Oxide,Manganese Oxide (MgO), or Aluminosilicate (Al2SiO5).
 7. The coolingsystem of claim 1, wherein the filter unit comprises a desiccant filterfor filtering dissolved water or free water from the refrigerant,wherein a filtering material of the desiccant filter is one or morefiltering materials selected from the group of Zeolite Scavengersorbents, calcium zeolites, sodium zeolites, potassium zeolites,magnesium zeolites, graphene oxide, and polymers.
 8. The cooling systemof claim 1, wherein the filter unit comprises a particle filter forfiltering particles from the refrigerant, wherein the particle filter isa stainless steel mesh or a magnet.
 9. A cooling system comprising arefrigerant cycle line for cycling refrigerant from at least acompressor unit for compressing gaseous refrigerant to a condenser unitfor condensing gaseous refrigerant to liquid refrigerant, from thecondenser unit to an expansion unit for expanding the liquidrefrigerant, from the expansion unit to an evaporator unit forevaporating the liquid refrigerant to gaseous refrigerant, and from theevaporating unit back to the compressor unit, wherein at least thecompressor unit comprises a refrigerant lubricated bearing arrangement.10. The cooling system of claim 10, wherein the refrigerant supply linebranches off from the refrigerant cycle line.
 11. The cooling system ofclaim 10, wherein the at least one filter comprises at least one of anacid filter, a desiccant filter, and a particle filter.
 12. The coolingsystem of claim 10, wherein the at least one filter is a combined filterunit of at least an acid filter and a desiccant filter for filteringacid and moisture from the refrigerant.
 13. The cooling system of claim10, wherein the at least one filter unit is a filter arrangement of aplurality of filter elements comprising an acid filter, a desiccantfilter, and a particle filter, wherein the acid filter is arrangedupstream of the desiccant filter and the particle filter and thedesiccant filter is arranged upstream of the particle filter.
 14. Thecooling system of claim 10, wherein the filter unit is adapted toabsorb, catch, or trap certain molecules from the refrigerant bychemical or physical adsorption.
 15. The cooling system of claim 10,wherein the filter unit comprises an acid filter for filteringhydrofluoric acids and/or hydrochloric acids from the refrigerant,wherein a filtering material of the acid filter comprises at least oneof Alumina (Al₂O₃), Silica (SiO2), Graphite Oxide, Graphene Oxide,Manganese Oxide (MgO), or Aluminosilicate (Al2SiO5).
 16. The coolingsystem of claim 10, wherein the filter unit comprises a desiccant filterfor filtering dissolved water or free water from the refrigerant,wherein a filtering material of the desiccant filter is one or morefiltering materials selected from the group of Zeolite Scavengersorbents, calcium zeolites, sodium zeolites, potassium zeolites,magnesium zeolites, graphene oxide, and polymers.
 17. The cooling systemof claim 10, wherein the filter unit comprises a particle filter forfiltering particles from the refrigerant, wherein the particle filter isa stainless steel mesh or a magnet.